A thin film transistor liquid crystal display (TFT-LCD) has been dominant in the current marker due to its small volume, low power consuming, no irradiation and so on.
An array substrate is one of the important components of the thin film transistor liquid crystal display, as shown by a cross-sectional structural view in FIG. 1, the array substrate mainly comprises a base substrate 10, a gate electrode 20, a gate insulation layer 30, an active layer 40, a source/drain metal layer comprising a source electrode 501 and a drain electrode 502, a protection layer 60 and a pixel electrode layer 70 provided on the base substrate 10.
An ON-state current of a thin film transistor can be expressed by
            I      on        =                            μ          eff                ⁡                  (                                    ɛ              ins                        ⁢                                          ɛ                0                            /                              t                ins                                              )                    ⁢              W        L            ⁢              (                              V            gs                    -                      V            th                          )            ⁢              V        ds              ,wherein μeff is an equivalent carrier mobility, tins is a thickness of the gate insulation layer,
            ɛ      ins        ⁢          ɛ      0            t    ins  is a capacitance of the gate insulation layer per unit area, W is a channel width, L is a channel length, Vgs is a gate-source voltage, Vds is a drain-source voltage and Vth is a threshold voltage. From above, it can be seen that the smaller the channel length, the larger the On-state current of the TFT. Herein, the channel length L is a distance between the source electrode and the drain electrode, e.g. as denoted by the double-arrow in FIG. 1.
However, during manufacturing the array substrate, due to a process limitation in the prior art, the channel length of the thin film transistor can generally be reduced to 3 μm-4 μm, which makes the ON-state current of the thin film transistor not very large.